Cocaine Dependence is associated with higher levels of impulsivity, both clinically and as measured by questionnaires and laboratory measures. We have found that impulsivity is associated with a poor outcome in the treatment of cocaine dependence. Further, there is evidence from our group and others that impulsivity is associated with decreased functioning of the neurotransmitter serotonin, and that serotonergic medication increases response to contingency management treatment for cocaine dependence. In light of the above data, we propose a treatment study to determine whether the serotonin reuptake inhibitor citalopram improves response to contingency management treatment of cocaine dependence. We also propose to measure serotonin and impulsivity to determine whether baseline serotonin function, and changes in impulsivity predict response to treatment. The Specific Aims of this Proposal Are: Aim 1. To determine whether chronic administration of the 5-HT reuptake inhibitor citalopram improves response to contingency management treatment of cocaine dependence. Hypothesis related to Aim 1: Cocaine Dependent subjects treated with citalopram will have a greater response to contingency management treatment for cocaine dependence than those treated with placebo. Aim 2. To measure pretreatment serotonin (5-HT) function using a citalopram neuroendocrine challenge and determine the relationship between 5-HT function and response to treatment in cocaine dependent subjects. Hypotheses related to Aim 2: 1. Citalopram will significantly increase plasma oxytocin and ACTH compared to placebo. 2. Within male and female cocaine dependent subjects, the neuroendocrine response to citalopram will inversely correlate with response to treatment with citalopram plus contingency management. Thus subjects with lower baseline serotonin function will show the greatest response to citalopram treatment for cocaine dependence. Aim 3. To measure impulsivity in subjects undergoing treatment for cocaine dependence using laboratory tasks to determine if changes in impulsivity predict response to treatment for cocaine dependence. Hypothesis related to Aim 3: Change in impulsivity as measured by laboratory tasks, will inversely correlate with length of subject retention and number of negative urine drug screens in subjects being treated for cocaine dependence.